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The synthesis and structural study of two benzothiazolyl azo dyes. X-ray crystallographic and computational study of azo-hydrazone tautomerism

The synthesis, FT-IR, 1H and 13C NMR, as well as crystal and molecular structure determined by single-crystal X-ray diffraction data, of two azo dyes derived from 6-aminobenzothiazole: 6-[(4-N, N-dimethylaminophenyl)diazenyl]benzothiazole (1) and 6-[(2-hydroxy-1-naphthyl)diazenyl]benzothiazole (2) are reported. Both dyes 1 and 2 are essentially planar with the exclusion of methyl groups in 1. Dye 1 exibits 100% E configuration regarding the orientation of the substituents about the central azo linkage. The single-crystal X-ray study of 2 is undertaken in order to established type of the tautomer present (hydrazone and azo) in the solid state and possible shifting in tautomeric equilibrium by the temperature variation (296 and 100 K). Density functional theory calculations have shown that the hydrazone tautomer is more stable than azo tautomer. The tautomeric equilibrium is shifted towards the hydrazone form and it is more pronounced at lower temperature.

benzothiazole ; azo dyes ; tautomerism ; XRD study ; DFT calculations

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